1. Field of the Invention
The invention relates to a thin-film evaporator including a heatable tubular evaporator body with an externally driven rotor equipped with essentially radially oriented vanes being disposed in the product charged interior of the evaporator body.
2. Description of the Related Art
Thin-film evaporator of the above-mentioned type are employed for the concentration of viscous, temperature sensitive and/or coating forming substances. They are all based on the principle of producing, with the aid of a rotating rotor, a thin layer of the product in the interior of a heated cylinder or cone so that the heat introduced through the cylinder wall leads to the evaporation of the liquid. The vapors need traverse only a short path through the product. Thus it is possible to concentrate solids containing liquids to high solids concentrations up to 80 weight % dry substance. The rotor is equipped with rigid vanes which are arranged with a narrow gap of a few millimeters from the heated wall or the rotor is equipped with movable wiper blades so that the product running over the heated walls of the evaporator body can be restricted to a thin film of product. When treating corrosive media, for example for the concentration of acids charged with solids, the corrosion problems cannot be solved with metal materials, particularly since the evaporator body must also be designed as a pressure vessel. Tests with enamel coatings are able to solve the corrosion problem only in special cases, particularly since it is practically impossible in larger units to perform the necessary mechanical work.